[Insight-users] Problem with Demons Variant Deformable Registration

[Nithiananthan, Sajendra]

Hello everyone,

I am trying to deformably register two images using the Demons algorithm.
Based upon the examples in the ITK User's Guide I attempted the registration
using Thirions original implementation and had good results after a
sufficient number of iterations. I then attempted the same registration
using the SymmetricForcesDemons implementation provided with ITK.  I found
that I do get convergence in fewer iterations, however, each iteration takes
much much longer to run (100-1000xlonger or worse) on my machine than the
original implementation.
After this, I created a Demons Registration filter which used
itkFastSymmetricForcesDemonsRegistrationFunction (a reimplementation of
SymmetricForcesDemonsFunction, but more efficient) . This runs at speeds
comparable to the original Demons implementation, and also converges in
fewer iterations, similar to SymmetricForcesDemons.  Unfortunately, the
image I get by using the deformation field produced from
FastSymmetricForceDemons suffers from degraded image quality: there is a
"chunkiness" in parts of the image (please see attached image).  This effect
noticeably reduces the quality of the image to the human eye, but does not
seem to have too much of a negative impact on the metric the algorithm is
calculating. This effect does not happen with the original Demons
implementation or SymmetricForces implementation.
I have examined the code for all three implementations and can not find the
source of the problem.  From the code, it is also not clear to me why
itkSymmetricForcesDemons runs so painfully slow compared to the other
implementations (it does however only run on one core compared to four for
the others).
Would anyone have any insights or suggestions?  The fast convergence of the
two SymmetricForces algorithms are great, but the incredibly slow running
speeds and image quality problems are a bit of a show stopper right now.
If it helps, I can send my sample data and code which produces the
registered images with degraded quality.
I got these results using InsightToolkit-3.2.0 compiled with MS Visual
Studio 8 on Windows XP 32bit.

Thank you very much,
Sajendra N.


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